(1) Field of the Invention:
The present invention relates to fibrous materials for reinforcing rubber products such as pneumatic tires, conveyor belts, belts, and hoses. More particularly, the invention relates to rubber-reinforcing fibrous materials having improved heat resisting adhesion for rubber.
(2) Related Art Statement:
As materials for reinforcing products such as tires, conveyor belts, belts, hoses, and air springs, fibrous materials are used in the form of filament chips, cords, cables, cord fabrics, or canvas. In order to reinforce such products as desired, it is important that these fibrous materials are firmly bonded to rubber. It is not an exaggeration to say that this determines use life of rubbery products and intended performances thereof.
Under the circumstances, in order to bond fibrous materials to rubber, there have favorably formerly been used adhesives in which a resin bondable to fibers, such as resorcinol-formaldehyde resin, urea-formaldehyde resin, or phenol-formaldehyde resin, is dispersed in rubber latex.
It is a common practice to use adhesives in such a manner that the adhesive is coated onto fibers, the adhesive and the fibers are bonded, the thus obtained fibrous material is buried in a compounded rubber, and then the compounded rubber is bonded to the fibrous material simultaneously with vulcanization of the compounded rubber. The adhesive used in this technique is called "rubber vulcanizing type adhesive".
However, since the weight of tires, etc. are being reduced in view of recent energy saving demands, there is a tendency that thermal input and dynamic input to be exerted upon products per unit weight becomes greater than before. For this reason, it is necessary to enhance thermal stability of strength, modulus, etc. and fatigue fracture resistance of various components constituting such products. Therefore, it is required that adhesion between the fibrous material and rubber is stable and firm enough to exhibit sufficient use life against such inputs.
However, although an amount of the resorcinol-formaldehyde resin in a conventional resorcinol-formaldehyde latex is increased to more firmly bond the rubber and the fibers through the adhesive, bonding force for the rubber side is lowered. On other hand, even if the bonding force for the rubber side is increased, the bonding force for the fiber side is in turn lowered. Ultimately, conventional adhesives did not satisfy the required performances mentioned above.
It is recited as other fault of the rubber vulcanizing type adhesive that the adhering force vigorously varies depending upon vulcanizing temperatures. That is, while rubbery products are vulcanized at low temperatures to satisfy various performances intended therefor in some cases, an amount of heat applied during vulcanization varies depending upon locations in the case of ununiformly shaped products such as tires, in which the thickness varies. Consequently, ununiform adhesion occurs in resulting products. Therefore, there sometimes occur troubles relating to rubber-fiber adhesion, such as separation, at locations where insufficient heat is applied.
When products such as tires, conveyor belts, etc. are subjected to accelerating tests under far more severer use conditions than as actually used on the market so as to ensure that they fully withstand their specified maximum use life span, the above-mentioned troubles tend to more frequently occur.
From the aforementioned point of view, it is necessary that adhesives used for bonding fibrous materials to rubber exhibit excellent thermal resistance and dynamic fatigue resistance, and that adhesion is less dependent upon the vulcanizing temperature. However, it is an actual situation that such an adhesive as satisfying the above requirements has not been discovered.